"Not much is going to change. He's a great dude, and he's very focused on what he does and everything else, and I'm sure this will bring out the best," Fatone, 35, told PEOPLE Thursday as he brought daughters Briahna and Kloey to see Batman Live in Los Angeles.

Timberlake and Biel know each other so well, Fatone adds, that they're destined to stay together.

"He's been with her for a long time, so it's basically a piece of paper," he said. "That's what me and my wife [Kelly Baldwin] were like, and we've been together over 18 years now."

Asked what advice he'd give Timberlake, who recently enjoyed a bachelor party in Las Vegas and Mexico, Fatone replied: "Just enjoy life, because it goes by way too fast. Look, I have an 11-year-old and a 2-year-old, and that just shows how quickly it goes."

This isn't the first time Fatone has offered Timberlake some life tips.

Last winter, following the couple's engagement, Fatone suggested, "It's the communication that really needs to drive that relationship," and advised them to "keep it happy, light and fun."

Fatone, of course, is in the midst of his own exciting drama – the all-star season of Dancing with the Stars. On that score, so far so good, he says.

"I feel great, and my stamina has been better than I expected, and it's been a blast so far," said Fatone. "I was sad to see Pamela [Anderson] go, I really was, because we really are all genuinely pulling for each other, believe it or not."